1. Field of the Invention
The present invention relates to fiber optic gyroscopes and, more particularly, to reusable, high stiffness, magnetic shielding therefor.
2. Description of Related Art and Other Considerations
A fiber optic gyroscope includes a fiber optic coil, which is conventionally mounted on a spool, and related components housed and secured within a shield of permeable ferromagnetic material which acts to protect the coil from undesirable electromagnetic energy that would otherwise deleteriously affect operation of the gyroscope. In one known construction, the shield comprises a two-component arrangement of a base shield and a cover shield, with the spool-mounted fiber optic coil being positioned on and bonded to the base shield. The base and the cover shields are also bonded together. Before bonding, shims are used to center the spool within the base shield, and to adjust the positioning of the cover shield in a level position. A bolt with washers is inserted through an opening in the cover shield and through the spool to secure the gyroscope to a mount.
This construction requires thirty-six assembly steps, involving the use of fixturing, shimming and semi-permanent bonding of the cover and base shields. A substantial amount of time is required to complete the assembly due to the need for extensive tooling and worker time, including a series of tooling/shimming steps and final securing of the cover and base shields together. Thereafter, when the device was tested and a defect was found, the failure was invariably found to be due to some gyroscopic malfunction. It was then necessary to separate the cover and base shields from one another to perform rework and repair on the internal components. Such separation of the shields always resulted in their destruction and furthermore caused damage to one or more of the internal components. The consequence was scrapping of damaged parts, and the need to perform additional rework and repair, with attendant reassembly time.
This known gyroscope is also subject to the production of resonant frequency and vibration problems with respect to the airframe to which it is attached. The airframe has a operational range of frequencies. The coupling of the cover shield solely to the lower shield and, thereby, to the remainder of the gyroscope assembly permits the cover shield to be exposed to vibrational forces and to the resultant production of resonant frequencies. Because of the construction of the above-described known gyroscope, its resonant frequencies were found to be too close to the range of airframe frequencies, which produced a potential for vibrationally induced gyroscopic failures, specifically, the gyroscope would not perform correctly and, therefore, would produce erroneous signals that are unrelated to the navigational inputs to the device.